Event-Call if board gets a message

Hello

Is there a possibilty to catch the moment, a message arrived on the board? (UART)
The board I use is:

--> Teensy 3.1 with soldered Crystal.
--> RTC doesn't support "millisec"

I should get these information, when the message arrived:

1: date
2: hours
3: minutes
4: sec
5: millisec!

I haven't any ideas how to get these information.. :frowning:

Could you help me pls?

Thanks

Narcisse97